Effect of antibiotics on extracellular protein level in Pseudomonas aeruginosa

• Increased amount of extracellular protein was detected in those Pseudomonas aeruginosa strains harbouring certain plasmids.
• Increased level of extracellular protein was detected in the presence of kanamycin or tetracycline.
• All antibiotics inhibited total activity of protease(s) except alkaline protease (AprA).
• Tetracycline and kanamycin interfered with AprA production.
• The effect of AprA on extracellular protein levels was limited.

Pseudomonas aeruginosa PAO1 organisms harbouring different plasmids were cultured in broths containing appropriate antibiotic(s). Extracellular proteins were more abundant in the presence of tetracycline or kanamycin than in the presence of other antibiotics. Zymography revealed that alkaline protease (AprA) production was interfered by these antibiotics. Extracellular proteins were not observed at the same level when AprA-deficient EG03 strains were cultured in the presence of different antibiotics. The extracellular protein levels were dependent on the antibiotics and plasmid derivative groups. Levels of extracellular protein were not significantly different between PAO1 (pBBR1MCS-5) and EG03 (pAprcomp-MCS5), and profiles of the extracellular proteome were comparable. In contrast, the level of EG03 (pBBR1MCS-MCS5) extracellular protein was higher than those observed in the other two strains. These results suggested that although AprA partially contributes to the alteration of extracellular protein level, the effect is limited.